Surface Patterning of Hydrogels for Programmable and Complex Shape Deformations by Ion Inkjet Printing

Abstract

Convenient patterning and precisely programmable shape deformations are crucial for the practical applications of shape deformable hydrogels. Here, a facile and versatile computer‐assisted ion inkjet printing technique is described that enables the direct printing of batched, very complicated patterns, especially those with well‐defined, programmable variation in cross‐linking densities, on one or both surfaces of a large‐sized hydrogel sample. A mechanically strong hydrogel containing poly(sodium acrylate) is first prepared, and then digital patterns are printed onto the hydrogel surfaces by using a commercial inkjet printer and an aqueous ferric solution. The complexation between the polyelectrolyte and ferric ions increases the cross‐linking density of the printed regions, and hence the gel sample can undergo shape deformation upon swelling/deswelling. The deformation rates and degrees of the hydrogels can be conveniently adjusted by changing the printing times or the different/gradient grayscale distribution of designed patterns. By printing appropriate patterns on one or both surfaces of the hydrogel sheets, many complex 3D shapes are obtained from shape deformations upon swelling/deswelling, such as cylindrical shell and forsythia flower (patterns on one surface), ding (patterns on both surfaces), blooming flower (different/gradient grayscale distributive patterns on one surface), and non‐Euclidean plates (different/gradient grayscale distributive patterns on both surfaces).

Enabling and Localizing Omnidirectional Nonlinear Deformation in Liquid Crystalline Elastomers

“…[1] Numerous approaches have been reported to spatially vary the mechanical properties of synthetic materials. [2][3][4][5] Often, these approaches have focused on assimilating the properties of multiple materials in a single structural element. These multimaterial composites, when rationally organized, materials, realizing localized deformation in films of continuous composition.…”

“…[7,11] Less appreciated, but equally compelling to functional end uses, is the nonlinear deformation of LCEs to load. [2][3][4][5] Often, these approaches have focused on assimilating the properties of multiple materials in a single structural element. Specifically, when the loading axis is parallel to the molecular orientation (the nematic "director"), the LCE exhibits a linear elastic response.…”

Shape changing hydrogels and their applications as soft actuators

“…Among the reported methods, photolithographic 55,56 and three-dimensional (3D) printing methods [57][58][59][60][61] can produce hydrogels with macroscale inhomogeneous structures by introducing a double-network hydrogel or inducing different orientations of additive cellulose fibrils, respectively. Photolithographic, 62-66 electrochemical ionprinting, [67][68][69][70] ion-transfer-printing (ITP), 50 and ion-inkjetprinting (IIP) 71 methods can prepare hydrogels with molecular scale inhomogeneity by introducing crosslinking gradients into as-prepared hydrogels.…”

Softening and Shape Morphing of Stiff Tough Hydrogels by Localized Unlocking of the Trivalent Ionically Cross‐Linked Centers

“…To the best our knowledge, this is the first invention of the softening of multivalent ion‐stiffened tough hydrogels via in situ chemical reduction. Importantly, there are several significant aspects of the current study to the field of hydrogel‐based shape morphing . First, soft structures can be precisely engineered into stiff structures by combining various surface patterning techniques.…”